Bill Gates’ publicly reported portfolio currently has 25 stock holdings in the latest available filings, while Steve Ballmer’s reported portfolio is generally tracked separately and is not captured in the same source here. Bill Gates’ holdings count comes from a recent portfolio filing that lists 25 total holdings, and another market summary also shows a similar low-20s count depending on how options and reporting dates are handled.

What that means

  • Bill Gates: about 25 stocks in public filings.
  • Steve Ballmer: I don’t have a verified current holdings count in the available source set for this answer, so I can’t give a reliable number without risking inaccuracy.

Important note

“Own” can mean different things:

  • number of different stocks held,
  • number of shares owned,
  • or the value of those holdings.

If you meant shares rather than stock positions, the answer would be very different, because Gates and Ballmer own large blocks of stock in a few names rather than a huge number of different companies.

TL;DR

Bill Gates is publicly reported as holding about 25 stocks. Steve Ballmer’s current stock count isn’t verified in the sources available for this response, so I can’t state a dependable number.